Study Finds Global Warming Has Accelerated Since 2015, Raising Pressure on Paris Goals

For years, scientists have warned the world is warming. A new study argues that in the past decade, it hasn’t just stayed on that path — it has sped up.

Warming rate may have nearly doubled

Global temperatures have been rising nearly twice as fast since the mid-2010s as they did in the late 20th century, according to research published March 6 in Geophysical Research Letters. After stripping out the effects of El Niño, volcanic eruptions and changes in solar output, the authors report a “strong and statistically significant acceleration of global warming since around 2015.”

If the finding holds up, it suggests the planet may be closing in on the Paris climate accord’s 1.5-degree Celsius limit sooner than many projections indicated, leaving less time to cut greenhouse gas emissions and prepare for worsening heat, floods and rising seas.

What the researchers analyzed

In the paper, titled “Global Warming Has Accelerated Significantly,” statistician Grant Foster and climate scientist Stefan Rahmstorf analyzed five major records of global surface temperature:

• NASA’s GISTEMP
• NOAA’s GlobalTemp
• the United Kingdom’s HadCRUT5
• the Berkeley Earth dataset
• the ERA5 reanalysis compiled by the European Centre for Medium-Range Weather Forecasts

Those records show the same broad story: steady warming since the 1970s, with year-to-year ups and downs. But Foster and Rahmstorf say much of that short-term wobble comes from natural influences that can temporarily warm or cool the planet.

“We can now demonstrate a strong and statistically significant acceleration of global warming since around 2015,” Foster said in a statement accompanying the study. Removing the natural swings, he said, “reduces the noise, making the underlying long-term warming signal more clearly visible.”

How they removed short-term “noise”

To do that, the researchers used a statistical technique they had applied in earlier work. They took monthly global temperature data and used lagged regression to estimate how much of each month’s reading could be explained by three factors:

• El Niño–Southern Oscillation (ENSO), which periodically warms or cools the tropical Pacific Ocean
• Volcanic eruptions, which can send sunlight-reflecting particles into the upper atmosphere
• Changes in solar radiation over the 11-year solar cycle

They then subtracted those influences to produce “adjusted” temperature series that, in theory, reflect mainly longer-term human-driven warming and slower natural changes.

When they examined the unadjusted data, the authors saw hints that the warming rate had increased recently, but not enough to clear conventional thresholds for statistical confidence. In two of the five datasets, evidence for a new change in trend after the 1970s barely exceeded 90% confidence.

The picture changed when they ran the same tests on the adjusted series.

A mid-2010s break point

Across all five records, a change-point analysis—a method used to detect shifts in the slope of a time series—identified an additional break around the mid-2010s. In four of the datasets, the change clustered near 2015; in HadCRUT5, it appeared slightly later, around 2021.

Before that point, from roughly 1970 to 2015, the world warmed at about 0.2°C per decade, the study found. Since then, the rate has jumped to roughly 0.35°C per decade, and approaches 0.4°C per decade in one of the authors’ preferred fits, which divides the record into 10-year segments.

“The adjusted data show an acceleration of global warming since 2015 with a statistical certainty of over 98 percent, consistent across all data sets examined and independent of the analysis method chosen,” Rahmstorf—a professor at the University of Potsdam and a researcher at the Potsdam Institute for Climate Impact Research in Germany—said in a statement.

In the paper’s preprint version, the authors wrote that with the new data, “there is no longer any doubt regarding a recent increase in the warming rate.”

To visualize the shift, Foster and Rahmstorf also applied a smoothing technique known as LOWESS, which acts like a low-pass filter on the global temperature series. It shows the underlying warming rate climbing from about 0.15 to 0.2°C per decade during 1980 to 2000 to more than twice that level in the most recent years.

What might be driving the acceleration

The study argues that the recent surge cannot be explained by El Niño, volcanoes or the sun alone. “The unusually rapid rise in global temperature over the last decade cannot be accounted for by the usual suspects,” the authors write, pointing instead to a change in the “forced response” of the climate system—how it responds to outside drivers such as greenhouse gases.

The paper does not pin down the precise cause of the acceleration, but other scientists have pointed to several likely contributors.

One leading hypothesis, advanced by former NASA scientist James Hansen and colleagues in earlier work, is that reductions in air pollution have played a role. Sulfur particles from ship exhaust and coal plants reflect sunlight and had been masking a portion of greenhouse warming. As countries tightened clean-air rules and the International Maritime Organization imposed stricter limits on sulfur in marine fuels, that cooling veil has thinned, revealing more of the heat trapped by carbon dioxide and other gases.

At the same time, concentrations of those heat-trapping gases have continued to rise. Carbon dioxide levels measured at Hawaii’s Mauna Loa Observatory, for example, passed 420 parts per million in recent years, far above preindustrial levels of about 280 ppm.

Scientific debate continues

Despite the strong language in the new study, not all climate scientists are ready to declare that global warming has entered a new, faster phase.

Michael Mann, a climatologist at the University of Pennsylvania known for his work reconstructing past temperatures, said he does not see evidence of a distinct step-change in the past decade.

Mann argues that the data are consistent with a warming rate that has been elevated since the 1970s—partly because of long-term cuts in aerosol pollution—with natural variability such as El Niño adding temporary spikes on top.

“The planet is warming at a roughly constant rate and that’s bad enough,” he said in an interview with CNN. “It will continue to do so until carbon emissions reach zero.”

Other experts strike a middle ground, saying the Foster and Rahmstorf analysis is careful but that more time is needed to see whether the apparent break around 2015 persists.

Katharine Hayhoe, a climate scientist at Texas Tech University and chief scientist for The Nature Conservancy, told reporters the study’s methodology was “careful and meticulous” and that climate models have long suggested warming could speed up as greenhouse gas concentrations increase. But Claudie Beaulieu, a climate statistician at the University of California, Santa Cruz, cautioned that uncertainties remain in fully removing the effects of El Niño, volcanic eruptions and solar changes.

Why it matters for Paris targets

The debate has high stakes for policymaking.

The World Meteorological Organization confirmed earlier this year that 2024 was the warmest year on record, with the global average temperature about 1.55°C above the 1850–1900 baseline often used as “preindustrial.” All 10 of the warmest years have occurred since 2015.

Under the 2015 Paris Agreement, nearly every country pledged to hold the increase in global average temperature “well below” 2°C above preindustrial levels and to pursue efforts to limit the rise to 1.5°C.

If the current higher warming rate continues, Foster and Rahmstorf estimate that the long-term global average will likely pass 1.5°C before 2030—earlier than many assessments that placed the breach in the mid-2030s. In their adjusted, smoothed series, they project the line being crossed as soon as late 2026, although that is not the formal definition used by the Intergovernmental Panel on Climate Change, which relies on multi-decade averages.

Even without adopting those specific dates, many scientists say the direction is clear: the window to meet the Paris targets is closing rapidly, and each additional fraction of a degree brings more extreme heat, heavier downpours, stronger storms and rising seas.

Impacts already visible

Those impacts are already visible. Heatwaves in 2023 and 2024 exposed hundreds of millions of people to dangerous temperatures, with spikes in heat-related hospitalizations and deaths. Global mean sea level has been rising faster in recent decades, driven by thermal expansion of warming oceans and melting ice sheets in Greenland and Antarctica.

An acceleration in surface warming, if sustained, would likely intensify those trends and further strain infrastructure designed under assumptions of more gradual change. Coastal defenses, water systems and power grids in many places were planned using older climate scenarios that assumed slower warming. Insurance companies and financial regulators have begun warning that faster-than-expected warming could increase economic losses and destabilize some markets.

The new study also carries implications for climate justice. Communities that contributed least to rising greenhouse gas levels—from low-lying island nations to heat-stressed neighborhoods in large cities—often have the least capacity to adapt. If the baseline climate is shifting more quickly, they could face more severe impacts before promised adaptation funding and loss-and-damage support materialize.

Rahmstorf has been blunt about what he sees as a gap between the science and the political response. In interviews, he has criticized governments that “basically just deny reality” despite mounting evidence of accelerating risks.

Whether the broader scientific community ultimately agrees that global warming has definitively shifted into a faster gear, the conclusion many researchers draw is the same: as long as emissions keep rising, so will temperatures.

The unresolved questions now are how fast that rise will be—and whether societies will move quickly enough to change it.